Broadband plate antenna



Sept. 1,1964 5.4. LAMBERTY 3,147,480

' BROA AND PLATE ANTENNA v Original Filed July 9, 1959 INVENTOR BERNARDJ. LAMBERTY BY) flw f/fw k ATTORNEY United States Patent Office3,147,480 Patented Sept. 1, 1964 3,147,480 BROADBAND PLATE ANTENNABernard J. Larnherty, Santa (liar-a, Caiif., assignor to SyivaniaElectric Products, Inc, a corporation of Delaware Original applicationJuly 9, 1959, Ser. No. 825,996, new Patent No. 3,050,750, dated Aug. 21,1962. Divided and this application May 17, 1962, Ser. No. 197,225 1Claim. (Cl. 343848) This invention relates to antennas, and moreparticularly to a class of physically small, broadband, mediumgainantennas. This application is a division of application S.N. 825,996,filed July 9, 1959, assigned to the assignee of this application, nowPatent No. 3,050,730.

A difficulty commonly experienced in antenna design is achievingbroadband operation while holding the physical size to a minimum. For abetter understanding of terms, broadband operation as used herein meansthe antenna requires no tuning to match its impedance to some relativeimpedance having a voltage standing wave ratio (VSWR) of less than 4.0to 1 over a frequency band at least three times the lowest operatingfrequency. Efforts in the past to build broadband small size antennasresulted in antenna configurations which are a function of angle onlyand not of length, that is, the antenna is impliedly infinite in extent.Spirals and modifications of spirals are examples of such antennaconfigurations. The difiiculty with this type of antenna is that thesize of the antenna must be at least a wavelength at the lowestoperating frequency. Furthermore, these antennas do not have a largebandwidth when operated over a ground plane and usually are complex anddifiicult to construct. Other types of antennas in this class areconical dipoles which must be at least a quarter wavelength high andhave rather limited bandwidth.

The class of antennas to which this invention relates operates over anextremely broad frequency band, in the order of 20 to 1, has amedium-gain characteristic, and is small in physical dimension-in theorder of a sixth of a wavelength or less at the lowest operatingfrequency. The fundamental antenna design on which this class ofantennas is based is a folded loaded unipole antenna characterized byseveral folds between the input end and the opposite end, the latter endbeing shorted to the ground plane over which the antenna is operated.The fingers comprising the folds are spaced apart and are made ofconducting material, the entire antenna generally resembling an end-fedglove. One embodiment comprises center-fed crossed rectangular plate andis one of a variety of different kinds of antennas which result fromoptimization of the desirable features of the basic structures. Theadvantages of small physical size relative to a wavelength, and uniformpatterns and impedance response are achievable in varying degrees withthis antenna.

An object of the invention is to provide a broadband antenna having asmall physical size with respect to a wavelength. Another object is theprovision of a broadband antenna having medium-gain characteristics andrelatively uniform radiation patterns, and whose largest physicaldimension is in the order of a sixth of a wavelength or less at thelowest operating design frequency. A further object is the provision ofa physically small antenna having relatively constant radiation patternand impedance characteristics over frequency bands in the order of 20 to1 or greater. Still another object is the provision of a broadbandplate-type antenna which can operate above a ground plane. A morespecific object is the provision of an antenna having a radiatingelement made of a solid or continuous rectangular conducting plate.

These and other objects of my invention will become apparent from thefollowing description of the various embodiments thereof, referencebeing bad to the accompanying drawings showing a perspective view of anantenna structure comprising two center-fed crossed rectangular plates.

Referring now to the drawing, antenna 10 comprises two center-fedrectangular plates 11 and 12 crossed at right angles to each other alongthe feed point and over ground plane 13. The center conductor 14 of thecoaxial feed line is joined to the lower edges of the plates at theirpoints of intersection. The effect of this configuration is that theradiation pattern minima of one plate are largely filled by theradiation pattern maxima of the other, since the plates are orthogonalto each other, as are the radiation pattern maxima and minima of asingle plate structure. Orthogonal placement of two such plates alsoresults in elimination of the undesirable lobes.

The VSWR of the cross-plate antenna 10 averages at about 3.0 to 1 over afrequency range of 20 to 1. H- plane patterns are omnidirectional towithin 3-db variation over the 20 to 1 frequency band. E-plane patternsare essentially the same as those of a single center-fed continuousrectangular plate antenna. The height of the crossed plate antenna 30 isapproximately one-eighth of a wavelength at the lowest operatingfrequency f Modifications, changes and improvements in the abovedescribed embodiment of my invention may be made by those skilled in theart without departing from the precepts of my invention. The scope ofthe invention, therefore, is defined in the appended claim.

I claim:

A high frequency antenna comprising a pair of continuous generallyrectangular plates of conducting material, said plates being mountedclose to and normal to a ground plane and intersecting each other alongthe axis of symmetry of each, and a transmission line connected to theedges of said plates at the point of intersection.

France Apr. 30, 1927 Switzerland Feb. 16, 1948

